In general, a resectscope is used for transurethral resection (TUR) and transcervical resection (TCR). The resectscope mainly includes, in a long, narrow and hollow sheath to be inserted into a body cavity, an optical scope (sometimes simply called scope), which is an endoscope for observation, and an electrode unit for resecting living body tissue.
As the resectscope, for example, Japanese Examined Utility Model Registration Application Publication No. 4-45694 discloses a resectscope apparatus an electrode for rigid scope surgical instrument having a rigid heat-resistance member between a distal end portion of an electric insulative member and an elemental wire. The rigid heat-resistance member is in contact with the periphery of the elemental wire. Thus, burns of the electric insulative member can be prevented.
When the resectscope is used for resecting the prostate, for example, D-sorbitol may be supplied which is insulating transparent liquid as a perfusion fluid for expanding the inside of a narrow cavity. Thus, the cavity is expanded, and a sheath of the resectscope can be inserted into the cavity.
Then, the surface of a lesion is observed by using a scope located within the sheath. At the same time, high frequency current passes through a treating electrode of an electrode unit located at a distal end portion opening of the sheath. By discharging, current flows from the treating electrode to an external electrode located outside of a body through the liquid filled within the cavity. Then, the operating portion is manipulated to move the treating electrode back and forth for treating the lesion.
Here, because the perfusion fluid filled within the cavity is an insulative liquid, the dispersion of current traveling from the treating electrode to the external electrode can be prevented. Thus, more efficient treatment can be performed.
However, when a treatment is performed by filling an insulative liquid within a cavity, and when the treating time is longer, the liquid is absorbed into a blood vessel, which may have bad influences on a human body. Therefore, the operation time is limited.
In order to overcome the problem, a physiological saline, which is a conductive liquid, may be filled within a cavity as a perfusion fluid. However, when the conductive liquid is filled within a cavity, current to flow from the treating electrode to the external electrode disperses through the liquid. Therefore, discharging does not occur on a lesion, which disadvantageously cannot achieve effective treatment.
Thus, Japanese Unexamined Patent Application Publication No. 2000-201946 discloses a resectscope apparatus including a treating electrode and a return electrode. The treating electrode is located in the vicinity of a long, narrow and hollow sheath distal end portion to be inserted into a body cavity filled with a conductive liquid. The treating electrode treats a body tissue by using high frequency cauterization current. The return electrode is located within the conductive liquid. The return electrode receives current from the treating electrode. An insulating portion is provided on at least a body tissue non-contact surface of the treating electrode. Thus, high frequency current supplied to the treating electrode within the cavity filled within the conductive liquid does not leak from the insulating portion on the body tissue non-contact surface of the treating electrode to the liquid. The high frequency current is efficiently discharged from a body tissue contact surface of the treating electrode in contact with a body tissue. The high frequency current flows to the return electrode.
However, in the resectscope apparatus according to Japanese Unexamined Patent Application Publication No. 2000-201946, a distance between the treating electrode and the return electrode is small. Therefore, when energized in the air or in a nonconductive liquid by mistake, excessively large voltage occurs. Then, an electrical breakdown may be produced between the electrodes disadvantageously.
The present invention was made in view of the above-described problems. It is an object of the present invention to provide a resectscope apparatus, which can properly control outputs by discriminating electrical characteristics of perfusion fluids.